1. Field of the Invention
The present invention relates to an ink storage container.
2. Description of the Related Art
Examples of the ink storage container include ink tanks for writing instruments and ink cartridges (tanks) for ink-jet printers. Such ink tanks have a mechanism for introducing outside air to the tanks according to the amount of ink consumed for writing and printing characters and images so that the consumption of the ink is not adversely affected by a change in pressure inside the tanks. Examples of such a mechanism include a mechanism including a simple hole formed as an inlet of outside air and a mechanism including a ventilation passage with a valve mechanism for providing ventilation as necessary.
However, with the mechanism including a simple hole formed as an inlet of outside air, the ink may leak through the hole. Moreover, in writing instruments and also in ink-jet printers, their ink-ejecting means such as nibs or printer heads receive water head pressure caused by the weight of ink (the pressure corresponds to force per horizontal unit area that is exerted on the bottom surface of a liquid column extending from the bottom surface to the liquid level). Therefore, with the mechanism including a simple hole formed as an inlet of outside air and with a mechanism including a membrane that allows gas to pass therethrough but does not allow liquid to pass therethrough, the water head-pressure can cause the ink to flow out from the ejection hole since the pressure inside the ink tanks or the ink cartridges is the same as the atmospheric pressure. Hence, an ink absorbing body such as sponge must be disposed in at least a part of an ink storage unit above the ink ejection hole to retain the ink.
However, when the ink absorbing body such as sponge is used to retain the ink, the amount of ink stored in the ink storage unit is less than the amount of ink stored in an ink storage unit that has the same volume as the above ink storage unit and does not include the ink absorbing body, and the number of printable characters is reduced accordingly.
Therefore, users need to replace the ink storage container frequently. In commercial products, the ink capacity of a black ink storage container is generally greater than those for other colors, and the large ink capacity is achieved by simply increasing the size of the storage container. However, this results in an increase in the size of printers. As described above, the conventional ink storage containers cause various inefficiencies. In view of this, various improvement techniques have been proposed based on the idea of using a small valve element.
For example, an ink storage container has been proposed in which a ventilation passage with a valve mechanism for providing ventilation as necessary is formed in an upper lid portion of the storage container so as to be substantially embedded therein. In this ink storage container, the reduction in the amount of stored ink, which occurs in the ink storage container having the ink absorbing body disposed thereinside, can be prevented, and the outflow of the ink can also be prevented.
A conventional technique for providing the ventilation passage with a valve mechanism for providing ventilation is described in, for example, Japanese Patent Application Laid-Open No. 2001-277777. The technique described in Japanese Patent Application Laid-Open No. 2001-277777 is related to an ink cartridge. Specifically, an interconnected porous body serving as a valve element is disposed in a concave-shaped valve-attaching portion formed in a lid-attaching portion, and a lid having a ventilation hole is placed on the porous body. A protruding portion having a slit-like opening is provided below a hole portion. The lid is welded and secured to the lid-attaching portion by ultrasonic welding, whereby the valve element is enclosed in the valve-attaching portion.
In the structure described above, an elastic material is basically used to form an interconnected porous body, and the interconnected porous body is compressed to substantially close the interconnected pores, whereby the valve element including a plurality of ventilation pores with valve covers is formed. In this manner, the ejection of the ink can be appropriately controlled, irrespective of whether the change in pressure is small or large.
Japanese Patent Application Laid-Open No. Hei 8-187874 discloses an ink tank including a one-way valve and a ventilation membrane disposed below the one-way valve. The ventilation membrane is air-permeable, and the surface thereof facing the ink has been subjected to liquid repellent treatment to inhibit or prevent the ink from passing therethrough. With such a ventilation membrane, the ink is prevented from flowing upward therethrough and adhering to the one-way valve.
In the valve element used in the ink storage container disclosed in Japanese Patent Application Laid-Open No. 2001-277777, the slit-like opening is formed in the side wall of the protruding portion. In this manner, the ink is prevented from adhering to the valve element. However, the valve element is always in communication with the ink side. Therefore, although the protruding portion is provided, the ink can come in contact with or adhere to the valve element when the ink storage container is reciprocally moved during printing or is tilted at a certain angle when carried. When the ink comes into contact with or adheres to the valve element, the interconnected ventilation pores are clogged with the ink, and therefore the ventilation properties deteriorate. As described above, the ink can come into contact with the valve element, and this causes a difficulty in appropriately controlling the ejection of the ink over a range of from a small pressure change to a large pressure change. In such a case, the ventilation cannot be appropriately controlled. For example, when the ink storage container is used as a cartridge of an ink-jet printer, the above difficulty can cause faint printing due to ink depletion or ink shortage or can cause ink leakage from the head or excessive ejection of the ink.
Moreover, when the lid is ultrasonically welded to the lid-attaching portion, the valve element is adversely affected by the heat and is thereby hardened. Therefore, the valve element itself undergoes thermal stress caused by the thermal deformation and can be deformed. The valve element must have an air flow control function that is provided by elastic deformation of the very fine interconnected pores caused by the pressure difference between the inside and outside of the ink storage container. However, in the above case, the air flow control function intrinsic to the valve element can deteriorate. Moreover, although the valve element itself does not allow the ink to pass therethrough, the ink may leak from the circumference of the valve element when the valve element is not properly held.
The valve element disclosed in Japanese Patent Application Laid-Open No. 2001-277777 is basically a very good valve element. Specifically, the valve element is small in size and can control pressure bidirectionally. In addition, unlike plate-like valves and rubber-made bell-like valves, the valve element does not suffer deterioration in its function due to adhesion of dust. However, the only drawback is that the effective area varies due to adhesion of liquid. Therefore, Japanese Patent Application Laid-Open No. 2001-277777 provides some measures. For example, when a valve element is used which is formed of a liquid repellent material, or when a valve element is used which is not formed of a liquid repellent material but has been subjected to liquid repellent treatment to impart liquid repellency thereto, the ventilation interconnected pores of the valve element can be prevented from being clogged with the ink. However, this is difficult to achieve for the following reasons. Specifically, when a liquid repellent material such as a fluorine-based material is used to produce the valve element, it is difficult to produce an interconnected porous body and a compressed porous body having good elasticity. Moreover, when a liquid repellent valve element is produced from a non-liquid repellent material by subjecting a preformed valve element to liquid repellent treatment, it is difficult to form a liquid repellent film that exhibits good adherence even when environmental conditions such as temperature and pressure are changed, when shocks and vibrations are applied, and as the film ages. Specifically, it is difficult to produce an interconnected porous body and a compressed porous body with a liquid repellent film that resists peeling.
The present inventors have conducted tests on ink storage containers including: a valve element subjected to liquid repellent treatment; and a protruding portion having a slit-like opening formed in the side wall thereof. Specifically, the ink storage containers have been produced according to the description in Japanese Patent Application Laid-Open No. 2001-277777. The test results (not being publicly known at the time of filing the subject application) have shown that a small amount of liquid first adheres to a very shallow part of the valve element, the adhering liquid infiltrates into the valve element as the valve element is repeatedly opened and closed, and finally the liquid disturbs the opening and closing operations of the valve element to cause a reduction and instability in performance. In the state in which a small amount of liquid adheres to a very shallow part of the valve element, if the temperature inside the ink storage container increases, the internal pressure increases. The increased internal pressure also causes the liquid to infiltrate into the valve element. Moreover, during intermittent use at long intervals, the degree of infiltration of the liquid into the valve element increases, and finally the opening and closing operations of the valve element is disturbed. The liquid repellent treatment applied to the valve element and the infiltration prevention mechanism such as the protruding portion have conventionally been considered to be adequate measures and can actually suppress the infiltration of liquid into the valve element to some extent. However, the test results have shown that these measures are insufficient to completely prevent the infiltration of liquid into the valve element that undergoes long-term changes in environmental conditions such as temperature and pressure changes and to maintain the function of the valve element for a long period of time. According to the tests, the inventors have recognized that it is not sufficient to employ the idea of “suppressing the infiltration of liquid into the valve element” as described in Japanese Patent Application Laid-Open No. 2001-277777 and that it is required to employ a novel idea of “completely preventing the infiltration of liquid into the valve element.”